LC4: Another Pen-and-Paper Cipher

Bruce Schneier mentioned the ElsieFour (LC4) cipher in a recent blog post: "LC4: Another Pen-and-Paper Cipher" 

ElsieFour (LC4) is a low-tech cipher that can be computed by hand; but unlike many historical ciphers, LC4 is designed to be hard to break. LC4 is intended for encrypted communication between humans only, and therefore it encrypts and decrypts plaintexts and ciphertexts consisting only of the English letters A through Z plus a few other characters. LC4 uses a nonce in addition to the secret key, and requires that different messages use unique nonces. LC4 performs authenticated encryption, and optional header data can be included in the authentication. The above (linked) paper defines the LC4 encryption and decryption algorithms, analyzes LC4's security, and describes a simple appliance for computing LC4 by hand.
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I tried this cipher using letter squares made from index card stock. The cipher, once you are familiar with it, is easy enough, but the movement of the squares is slow (at least when using squares made from index cards).